Low-temperature curing enameled wire and preparation method thereof

Abstract

The invention provides a low-temperature curing polyamide-imide varnish and a preparation method and application thereof.The polyamide-imide varnish is prepared from aromatic tricarboxylic acid anhydride, aromatic diisocyanate and a compound organic solvent, and the compound organic solvent comprises a first organic solvent and a second organic solvent, the first type of organic solvent comprises any one or a combination of at least two of dimethyl sulfoxide, N-dimethylacetamide, N-methyl pyrrolidone or gamma-butyrolactone, and the second type of organic solvent comprises aliphatic polyester and / or aliphatic cyclic ketone; by selecting the specific parts of the compound organic solvent, the obtained polyamide-imide varnish has long-term storage stability and lower curing temperature, and meanwhile, a paint film formed after curing also has excellent limit performance and mechanical performance.

Description

[0001] This application is a divisional application. The application number of the parent application is 202410775667.2, the application date is June 14, 2024, and the name of the invention is "A low-temperature curing polyamide-imide varnish and its preparation method and application". Technical Field

[0002] The invention belongs to the technical field of coatings, and in particular relates to a low-temperature curing polyamide-imide varnish and a preparation method and application thereof. Background Art

[0003] Polyamide-imide is widely used in protective layers of various substrates due to its excellent thermodynamic properties, electrical properties and chemical stability, such as high-temperature resistant insulating coatings for white appliances, high-temperature resistant varnishes for enameled wires, and insulating electrical tapes.

[0004] At present, conventional polyamide-imide is prepared by high-temperature condensation of trianhydride and isocyanate in polar solvents, and commonly used polar solvents include organic solvents such as NMP and DMAc. For example, CN101397477A discloses a wire enamel, especially a wire enamel with high temperature resistance; the invention adopts a method of synthesizing polyamide-imide wire enamel by reacting trimellitic anhydride and isocyanate in a polar solvent, the ratio of raw materials MDI and TMA used in the invention can be MDI / TMA=1:0.85~1.05, the amount of solvent added in the invention is MDI / solvent=1:5.0~10.0, and the ratio of added diluent can be MDI / diluent=1:1.5~4.5; the reaction process of the invention does not need to add a catalyst, and during the high-temperature baking process, no curing agent is required to close the ring; the process flow of the invention is short and the operation is simple, and the synthetic PAI solution has the advantages of low viscosity and stable storage.

[0005] However, the solvents such as NMP and DMAc used in the above invention have high boiling points and require higher processing temperatures during the curing process, which is not conducive to economy; although the curing temperature can be lowered by adding aromatic hydrocarbon solvents, the amount of aromatic hydrocarbons added is very limited, and the addition of aromatic hydrocarbons will greatly increase the viscosity and storage stability of the slurry, which is not conducive to subsequent processability; at the same time, this type of solvent contains nitrogen, and during the high-temperature processing process, the solvent will evaporate and decompose or partially decompose, producing a large amount of nitrogen oxides, which is not conducive to environmental protection.

[0006] Therefore, developing a polyamide-imide varnish with low curing temperature and excellent storage performance is still a technical problem that needs to be urgently solved in the art. Summary of the invention

[0007] In view of the deficiencies in the prior art, the object of the present invention is to provide a low-temperature curing polyamideimide varnish and a preparation method and application thereof, wherein the polyamideimide varnish has long-term storage stability and a low curing temperature, and the paint film formed after curing has excellent insulation and mechanical properties.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a low-temperature curing polyamide-imide varnish, wherein the raw materials for preparing the polyamide-imide varnish include aromatic tricarboxylic anhydride, aromatic diisocyanate and a composite organic solvent;

[0010] The composite organic solvent includes a first type of organic solvent and a second type of organic solvent;

[0011] The first type of organic solvent includes any one or a combination of at least two of dimethyl sulfoxide (DMSO), N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP) or γ-butyrolactone;

[0012] The second type of organic solvent includes aliphatic polyesters and / or aliphatic cyclic ketones.

[0013] The present invention selects a specific composite organic solvent as the reaction medium of aromatic tricarboxylic anhydride and aromatic diisocyanate, so that the obtained polyamide-imide varnish has long-term storage stability and a lower curing temperature, and the paint film formed after curing has excellent insulation and mechanical properties; at the same time, the organic solvent volatilized during the curing process has a lower nitrogen content or no nitrogen in the waste gas after incineration treatment, which is more beneficial to environmental protection.

[0014] It should be noted that the "low-temperature curing polyamide-imide varnish" mentioned in the present invention refers to a polyamide-imide varnish having a curing temperature not higher than 400°C.

[0015] Preferably, the aromatic tricarboxylic anhydride includes any one of trimellitic anhydride, benzophenone tricarboxylic anhydride or diphenylmethane tricarboxylic anhydride, or a combination of at least two thereof.

[0016] Preferably, the aromatic diisocyanate includes any one or a combination of at least two of 4,4′-diphenylmethane diisocyanate, toluene diisocyanate, naphthalene diisocyanate, xylylene diisocyanate, biphenyl diisocyanate, diphenyl sulfone diisocyanate or diphenyl ether diisocyanate.

[0017] Preferably, the molar ratio of the acidic group to the isocyanate group in the preparation raw material is (0.95-1.05):1, for example, 0.96:1, 0.97:1, 0.98:1, 0.99:1, 1:1, 1.01:1, 1.02:1, 1.03:1 or 1.04:1, etc.

[0018] Preferably, the mass ratio of the first organic solvent to the second organic solvent is (1-9):(9-1), for example, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1 or 9:1, etc.

[0019] Preferably, the composite organic solvent includes a combination of the first type of organic solvent, an aliphatic polyester and an aliphatic cyclic ketone. The combination of the three organic solvents can better dissolve polyamideimide, so that it has better storage stability and better insulation performance after curing.

[0020] Preferably, the mass ratio of the aliphatic polyester to the aliphatic cyclic ketone is 1:(0.1-10), for example, 1:0.1, 1:0.5, 1:1, 1:2, 1:4, 1:6, 1:8 or 1:10, etc.

[0021] Preferably, the aliphatic polyester includes any one of propylene glycol monomethyl ether acetate (PGMEA), propylene glycol methyl ether propionate, methyl glycol ethyl ether acetate, propylene glycol ethyl ether acetate, ethylene glycol ethyl acetate, ethoxyethyl acetate, 1,2-propylene glycol diacetate, ethylene glycol diacetate, 2,3-butanediol diacetate, diethoxyethyl acetate, dimethoxymethyl acetate, methyl 4-methoxybutyrate, methyl methoxyacetate, diethyl ethyl malonate, tert-butyl ethyl malonate or dimethyl malonate, or a combination of at least two thereof.

[0022] Preferably, the aliphatic cyclic ketone includes any one or a combination of at least two of cyclopentanone, cyclohexanone (CYC), 2-methylcyclopentanone, 1,3-cyclopentanedione, 2-methyl-1,3-cyclopentanedione, 2-ethylcyclopentanone, 2,2-dimethylcyclopentanone, 4-methylcyclohexanone, 1,3-cyclohexanedione, 4-propylcyclohexanone, 4-tert-butylcyclohexanone, 4-ethylcyclohexanone, 2-methyl-1,3-cyclohexanedione, 1,4-cyclohexanedione, p-methoxycyclohexanone, 4,4-dimethylcyclohexanone, 2,2-dimethylcyclohexanone, 5,5-dimethyl-1,3-cyclohexanedione or 5-methylcyclohexane-1,3-dione.

[0023] Preferably, the preparation raw materials also include aromatic diacids.

[0024] Preferably, the aromatic diacid includes any one of terephthalic acid, isophthalic acid, biphenyl diphthalic acid or 4,4'-dicarboxylic acid diphenyl ether or a combination of at least two thereof.

[0025] Preferably, the solid content of the polyamideimide varnish is 20-45%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, 42% or 44%, etc.

[0026] In a second aspect, the present invention provides a method for preparing the polyamideimide varnish as described in the first aspect, the preparation method comprising: reacting an aromatic diisocyanate, an aromatic tricarboxylic anhydride and optionally an aromatic diacid in a composite organic solvent to obtain the polyamideimide varnish.

[0027] Preferably, the reaction is carried out under gradient heating conditions.

[0028] Preferably, the gradient heating method comprises: first heating the system to 40-100°C (for example, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C or 90°C, etc.), keeping the temperature for reaction for 1-5h (for example, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h or 4.5h, etc.), then heating to 110-170°C (for example), keeping the temperature for reaction for 3-15h, to complete the gradient heating.

[0029] In a third aspect, a low temperature curing enameled wire is provided, wherein the low temperature curing enameled wire comprises a conductor and the polyamide-imide varnish as described in the first aspect which is coated on the outside of the conductor after curing.

[0030] It should be noted that the "low-temperature curing enameled wire" mentioned in the present invention refers to an enameled wire whose curing temperature of the polyamide-imide varnish coated on the outside of the conductor is not higher than 450°C.

[0031] Preferably, the curing temperature is not higher than 400°C, for example 400°C, 390°C, 380°C, 370°C, 360°C or 350°C, etc.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] (1) The raw materials for preparing the polyamide-imide varnish provided by the present invention include aromatic tricarboxylic anhydride, aromatic diisocyanate and a composite organic solvent, wherein the composite solvent includes a first type of organic solvent and a second type of organic solvent, wherein the first type of organic solvent includes any one or a combination of at least two of dimethyl sulfoxide, N-dimethylacetamide, N-methylpyrrolidone or γ-butyrolactone, and the second type of organic solvent includes aliphatic polyesters and / or aliphatic cyclic ketones; by selecting the above-mentioned specific portion of the composite organic solvent, the obtained polyamide-imide varnish has good compatibility before curing, and thus has long-term storage stability, and also has a lower curing temperature, thereby effectively reducing the processing temperature of the enameled wire, and will not reduce the excellent mechanical properties and insulation properties of the polyamide-imide varnish itself;

[0034] (2) In the process of preparing the insulating wire, the amount of nitrogen oxides contained in the volatilized organic solvent after incineration is much lower than that of the existing products, which is beneficial to the environment;

[0035] (3) The low-temperature curing polyamide-imide paint provided by the present invention can be used as a topcoat or a primer, and can be used alone or in combination with conventional polyimide, polyamide-imide, or polyester-imide paints. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0037] Unless otherwise specified, the raw materials involved in the following specific embodiments of the present invention are all conventional materials in the field and can be purchased commercially; at the same time, the designed test methods and the test instruments used are also common test methods and commonly used test instruments in the field.

[0038] Example 1

[0039] A low-temperature curing polyamide-imide varnish, the preparation method of which comprises: adding 12 kg NMP, 1 kg PGMEA and 0.5 kg CYC into a 30 L reactor, then adding 5.091 kg diphenylmethane diisocyanate, stirring and heating to 80° C., adding 3.909 kg trimellitic anhydride into the reactor, maintaining the system temperature at 80° C., and reacting for 3 hours;

[0040] Then, 4 kg of PGMEA was added into the reactor, and the temperature was raised to 90° C. for reaction for 3 h. Then, the temperature of the system was raised to 150° C. for reaction for 2 h to obtain the low-temperature curing polyamide-imide varnish.

[0041] Example 2

[0042] A low-temperature curing polyamide-imide varnish, the preparation method of which comprises: adding 8kg NMP, 3.5kg PGMEA and 0.5kg CYC into a 30L reactor, then adding 5.091kg diphenylmethane diisocyanate, stirring and heating to 80°C, adding 3.909kg trimellitic anhydride into the reactor, maintaining the system temperature at 80°C, and reacting for 3h;

[0043] Then, 4 kg of PGMEA was added into the reactor, and the temperature was raised to 90° C. for reaction for 3 h. Then, the temperature of the system was raised to 150° C. for reaction for 2 h to obtain the low-temperature curing polyamide-imide varnish.

[0044] Example 3

[0045] A low-temperature curing polyamide-imide varnish, the preparation method of which comprises: adding 6kgNMP, 5.5kgPGMEA and 0.5kgCYC to a 30L reactor, then adding 5.091kgdiphenylmethane diisocyanate, stirring and heating to 80°C, adding 3.909kgtrimmellitic anhydride to the reactor, maintaining the system temperature at 80°C, and reacting for 3h;

[0046] Then, 4 kg of PGMEA was added into the reactor, and the temperature was raised to 90° C. for reaction for 3 h. Then, the temperature of the system was raised to 150° C. for reaction for 2 h to obtain the low-temperature curing polyamide-imide varnish.

[0047] Example 4

[0048] A low-temperature curing polyamide-imide varnish, which differs from Example 2 in that an equal amount of DMAc is used to replace NMP, and other substances, amounts and steps are the same as those in Example 2.

[0049] Example 5

[0050] A low-temperature curing polyamide-imide varnish, the preparation method of which comprises: adding 8kg DMAc, 3.5kg PGMEA and 0.5kg CYC into a 30L reactor, then adding 5.115kg diphenylmethane diisocyanate, stirring and heating to 80°C, adding 3.545kg trimellitic anhydride and 0.34kg isophthalic acid into the reactor, maintaining the system temperature at 80°C, and reacting for 3h;

[0051] Then, 4 kg of PGMEA was added into the reactor, and the temperature was raised to 90° C. for reaction for 3 h. Then, the temperature of the system was raised to 150° C. for reaction for 2 h to obtain the low-temperature curing polyamide-imide varnish.

[0052] Example 6

[0053] A low-temperature curing polyamide-imide varnish, the preparation method of which comprises: adding 8kg NMP and 2kg PGMEA to a 30L reactor, then adding 5.091kg diphenylmethane diisocyanate, stirring and heating to 80°C, adding 3.909kg trimellitic anhydride to the reactor, maintaining the system temperature at 80°C, and reacting for 3h;

[0054] Then, 4 kg of PGMEA was added into the reactor, and the temperature was raised to 90° C. for reaction for 3 h. Then, the temperature of the system was raised to 150° C. for reaction for 2 h to obtain the low-temperature curing polyamide-imide varnish.

[0055] Example 7

[0056] A low-temperature curing polyamide-imide varnish, which differs from Example 6 in that DMAc is used to replace NMP to obtain the low-temperature curing polyamide-imide varnish, and other substances, amounts and steps are the same as those in Example 6.

[0057] Example 8

[0058] A low-temperature curing polyamide-imide varnish, the preparation method of which comprises: adding 8.5 kg NMP and 4.25 kg CYC to a 30 L reactor, then adding 5.091 kg diphenylmethane diisocyanate, stirring and heating to 80° C., adding 3.909 kg trimellitic anhydride to the reactor, maintaining the system temperature at 80° C., and reacting for 3 hours;

[0059] Then, 4.25 kg of CYC was added to the reactor, and the temperature was raised to 90° C. for reaction for 3 h. Then, the temperature of the system was raised to 150° C. for reaction for 2 h to obtain the low-temperature curing polyamide-imide varnish.

[0060] Example 9

[0061] A low-temperature curing polyamide-imide varnish, which differs from Example 8 in that DMAc is used to replace NMP, and other substances, amounts and steps are the same as those in Example 8.

[0062] Comparative Example 1

[0063] A low-temperature curing polyamide-imide varnish, the preparation method of which comprises: adding 12kgNMP to a 30L reactor, then adding 5.091kg diphenylmethane diisocyanate, adding 3.909kg trimellitic anhydride to the reactor while stirring and heating to 80°C, maintaining the system temperature at 80°C, reacting for 3h, then adding 4kg NMP to the reactor, heating to 90°C, reacting for 3h, then heating the system temperature to 150°C, reacting for 2h, to obtain the low-temperature curing polyamide-imide varnish.

[0064] Comparative Example 2

[0065] A low-temperature curing polyamide-imide varnish, the preparation method of which comprises: adding 12kg DMAc to a 30L reactor, then adding 5.091kg diphenylmethane diisocyanate, adding 3.909kg trimellitic anhydride to the reactor while stirring and heating to 80°C, maintaining the system temperature at 80°C, reacting for 3h, then adding 4kg DMAc to the reactor, heating to 90°C and reacting for 3h, then heating the system temperature to 150°C and reacting for 2h, to obtain the low-temperature curing polyamide-imide varnish.

[0066] Comparative Example 3

[0067] A low-temperature curing polyamide-imide varnish, the preparation method of which comprises: adding 8kgNMP and 4kgDMAc into a 30L reactor, then adding 5.091kgdiphenylmethane diisocyanate, adding 3.909kgtrimmilitric anhydride into the reactor while stirring and heating to 80°C, maintaining the system temperature at 80°C, reacting for 3h, then adding 4kgDMAc into the reactor, heating to 90°C and reacting for 3h, then heating the system temperature to 150°C and reacting for 2h, to obtain the low-temperature curing polyamide-imide varnish.

[0068] Comparative Example 4

[0069] A low-temperature curing polyamide-imide varnish, the preparation method of which comprises: adding 12kg PGMEA to a 30L reactor, then adding 5.091kg diphenylmethane diisocyanate, adding 3.909kg trimellitic anhydride to the reactor while stirring and heating to 80°C, maintaining the system temperature at 80°C, reacting for 3h, then adding 4kg PGMEA to the reactor, heating to 90°C, reacting for 3h, then heating the system temperature to 150°C, reacting for 2h, to obtain the low-temperature curing polyamide-imide varnish.

[0070] Comparative Example 5

[0071] A viscous mixture, the preparation method of which comprises: adding 12.75 kg of CYC to a 30 L reactor, then adding 5.091 kg of diphenylmethane diisocyanate, adding 3.909 kg of trimellitic anhydride to the reactor while stirring and heating to 80° C., maintaining the system temperature at 80° C., reacting for 3 hours, then adding 4.25 kg of CYC to the reactor, heating to 90° C. and reacting for 3 hours, then heating the system temperature to 150° C. and reacting for 2 hours to obtain a viscous mixture.

[0072] Comparative Example 6

[0073] A low-temperature curing polyamide-imide varnish, the preparation method of which comprises: adding 8.5kg PGMEA and 4.25kg CYC into a 30L reactor, then adding 5.091kg diphenylmethane diisocyanate, adding 3.909kg trimellitic anhydride into the reactor while stirring and heating to 80°C, maintaining the system temperature at 80°C, reacting for 3h, then adding 4.25kg CYC into the reactor, heating to 90°C and reacting for 3h, then heating the system temperature to 150°C and reacting for 2h, to obtain the low-temperature curing polyamide-imide varnish.

[0074] Application Example 1

[0075] A low-temperature curing insulated wire, comprising a copper conductor with a diameter of 0.65 mm and a primer layer and a topcoat layer sequentially coated on the outside of the copper conductor;

[0076] The primer is a commercially available polyamide-imide paint (BOYAAIP 36UN); the topcoat material is the low-temperature curing polyamide-imide varnish provided in Example 1;

[0077] The preparation process of the low-temperature curing insulated wire provided in this application example is as follows: using the Sun H5000-1T-20D enameled wire machine, the process parameters are as follows: oven inlet: 300°C, oven middle: 350°C, oven outlet: 380°C, and the line speed is 18m / min.

[0078] Application Examples 2 to 9

[0079] A low-temperature curing insulated wire, which differs from Application Example 1 in that the low-temperature curing polyamide-imide varnish provided in Examples 2 to 9 is used to replace the low-temperature curing polyamide-imide varnish provided in Example 1, and other processes, conditions and parameters are the same as those in Application Example 1.

[0080] Comparative Application Examples 1 to 6

[0081] A low-temperature curing insulated wire, which differs from Application Example 1 in that the polyamide-imide varnish provided by Comparative Examples 1 to 6 is used to replace the low-temperature curing polyamide-imide varnish provided by Example 1, and other processes, conditions and parameters are the same as those of Application Example 1.

[0082] Performance Test:

[0083] (1) Test on polyamide-imide varnish

[0084] ① Solid content: Take an aluminum foil plate with a diameter of 60mm and weigh it as m0; take 1±0.1g of paint sample and put it in the aluminum plate, weigh the weight of the aluminum plate plus paint as m1; put the aluminum plate containing paint in a blast oven at 180±5℃, take it out after 1h, and weigh the mass of the aluminum plate containing paint as m2; Solid content = (m2-m0) / (m1-m0)×100%;

[0085] ②Viscosity: Use American Brookfield cone and plate viscometer to test the viscosity of the paint at 25°C;

[0086] ③Appearance: visual observation;

[0087] ④ Storage stability: Observe whether the paint is stratified after being placed at room temperature for 30 days.

[0088] The varnishes provided in Examples 1 to 9 and Comparative Examples 1 to 6 were tested according to the above test method. The test results are shown in Table 1:

[0089] Table 1

[0090]

[0091] From the data in Table 1, we can see that:

[0092] (1) The polyamide-imide varnishes provided in Examples 1 to 9 have a solid content of 27.3 to 32.4%, a viscosity of 1530 to 2580 cp, and are all brown-black transparent liquids in appearance. The storage stability is very uniform, and according to the viscosity comparison of Examples 1 to 3, it can be seen that as the amount of the second type of solvent increases, the viscosity of the obtained polyamide-imide varnish gradually increases;

[0093] (2) The polyamide-imide varnishes provided in Comparative Examples 1 to 3 contain only the first type of solvent, and the overall viscosity is low, while the polyamide-imide varnishes provided in Comparative Examples 4 to 6 contain only the second type of solvent, and the viscosity is too high and the storage stability is poor. After being placed at room temperature for 30 days, the paint was observed to be stratified and precipitated.

[0094] (2) Testing of insulated wires

[0095] ① Elongation: Tested in accordance with the test method provided in the national standard "GB / T 4074.3-2008";

[0096] ② Paint film continuity: The leakage test is carried out according to the test method provided by the national standard "GB / T4074.5-2008";

[0097] ③ Pressure resistance: Test according to the test method provided in the national standard "GB / T 4074.21-2018" to test whether it will be softened and broken down at 400°C;

[0098] ④ Adhesion: Test according to the test method provided in the standard "JB / T 4279.6";

[0099] ⑤Dielectric loss: Test according to the test method provided in the standard "JB / T 4074.3-2008";

[0100] ⑥ Stretch 15% 1d winding: Test according to the test method provided in the standard "GB / T6109";

[0101] ⑦ Voltage: Test according to the test method provided in the standard "GB / T6109".

[0102] According to the above test method, the low temperature curing insulated wires provided in Examples 1 to 9 and Comparative Application Examples 1 to 6 were tested, and the test results are shown in Table 2:

[0103] Table 2

[0104]

[0105]

[0106] In Table 2, “ / ” indicates that the test cannot be performed.

[0107] From the data in Table 2, we can see that:

[0108] (1) The voltage value of the insulated wire provided in Application Examples 1 to 5 is 7.4 to 7.6 cp, the elongation is as high as 37 to 39%, no holes are found in the paint film continuity test, no cracks are found in the winding after stretching 15% for 1d, no breakdown is found in the voltage resistance test, the adhesion is as high as 7.3 to 7.4 N, and the dielectric loss is 282.7 to 296.4 ° C. Under the same process conditions, the combination of the first type of solvent and the second type of solvent is beneficial to reducing the curing temperature of the polyamide-imide varnish, thereby increasing the dielectric loss of the obtained insulated wire and reducing its energy consumption. At the same time, the addition of the second type of solvent can also effectively reduce the amount of nitrogen-containing solvent, ensuring performance while reducing the generation of nitrogen oxides, which is beneficial to environmental protection.

[0109] (2) Compared with Application Example 1, the insulated wires provided in Comparative Application Examples 1 to 3 all cracked in the 15% 1d winding test and were punctured in the voltage resistance test, indicating that the winding property and voltage resistance are poor.

[0110] (3) Compared with Application Example 1, since the polyamide-imide varnishes provided in Comparative Examples 4 to 6 have too high a concentration, insulated wires cannot be made for the next step of testing.

[0111] (4) Compared with Application Example 1, the dielectric loss of the insulated wires provided by Application Examples 6 to 9 is also deteriorated, indicating that the combination of the first type of organic solvent, aliphatic polyester and aliphatic cyclic ketone has a better effect.

[0112] The applicant declares that the present invention illustrates a low-temperature curing polyamide-imide varnish and its preparation method and application through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A low temperature curing enameled wire, characterized in that: The low-temperature curing enameled wire comprises a copper conductor and a primer layer and a topcoat layer sequentially coated on the outside of the copper conductor; The topcoat layer is polyamide-imide varnish; The raw materials for preparing the polyamide-imide varnish include aromatic tricarboxylic anhydride, aromatic diisocyanate, aromatic diacid and a composite organic solvent; The composite organic solvent includes a first type of organic solvent and a second type of organic solvent; The first type of organic solvent includes any one or a combination of at least two of dimethyl sulfoxide, N-dimethylacetamide, N-methylpyrrolidone or γ-butyrolactone; The second type of organic solvent includes aliphatic polyesters and / or aliphatic cyclic ketones; The aromatic diacid includes any one of terephthalic acid, isophthalic acid, biphenyl diphthalic acid or 4,4'-dicarboxylic acid diphenyl ether or a combination of at least two thereof.

2. The low temperature curing enameled wire according to claim 1, characterized in that: The primer layer is polyamide-imide paint BOYAAIP 36UN.

3. A low temperature curing enameled wire according to any one of claims 1 to 2, characterized in that: The preparation method of the polyamide-imide varnish comprises the following steps: Aromatic diisocyanate, aromatic tricarboxylic anhydride, aromatic diacid and a composite organic solvent are mixed and reacted to obtain the polyamideimide varnish.

4. The low temperature curing enameled wire according to claim 3, characterized in that: The diameter of the copper wire is 0.65 mm.

5. A method for preparing a low temperature curing enameled wire according to any one of claims 1 to 4, characterized in that: The steps include: The copper conductor, primer and topcoat were prepared by using a Sun H5000-1T-20D enameled wire machine to obtain a low-temperature curing enameled wire.

6. The method for preparing a low temperature curing enameled wire according to claim 5, characterized in that: The process parameters of the Sun H5000-1T-20D enameled wire machine are: oven inlet: 300°C, oven middle: 350°C, oven outlet: 380°C, line speed: 18m / min.

Images